Considerable effort has been expended to identify the characteristics of quality jet fuel that is safe and reliable for jet plane transportation. The critical test for jet fuel is the JFTOT or Jet Fuel Thermal Oxidation Test and the process for such testing is described in ASTM Standard D3241. Consider that the fuel must be refined, shipped, stored, and transferred to airplanes on the ground at ordinary conditions, but also must remain stable, water free and reliable at low pressure and the ultra-low temperatures of high altitude flight prior to being subject to very high temperatures in the fuel delivery system to the jet engine. So, low oxidative thermal stability makes jet fuel vulnerable to forming precipitates in the fuel delivery system which may lead restrictions and blockages of flow. Low thermal stability of jet fuel is simply unacceptable. Low thermal stability is caused by contamination of certain organic compounds such as olefins and heterocyclic compounds along with metals including copper and zinc among others.
The conventional non-hydrotreating based procedures for removing these contaminants is by passing the raw kerosene or jet fuel through a sorbent drum filled with a silica or clay sorbent. The sorbent captures and adheres to both the organic and metallic contaminants. However, in time, the sorbent becomes saturated and its adsorbent capacity is used up, the contaminants begin to pass through the drum with the jet fuel. The finishing or polishing of the jet fuel is incomplete and the adsorbent must be replaced prior to such contamination break through. The sorbent, once saturated with these chemicals, is typically disposed as hazardous material which can be very expensive. The sorbent is sufficiently special to not be inexpensive, but the cost of disposal as a hazardous waste adds considerably to the cost of producing finished jet fuel.
While any replacement process for cleaning up the residual contaminants in jet fuel must be able to perform that function as well as the current process, but any cost savings within the clay sorbent life-cycle would be valuable and durable to refiners.